This application claims priority under U.S.C. xc2xa7xc2xa7119 and/or 365 to 9902370-7 filed in Sweden on Jun. 22, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to a method for radio communication. In particular, the invention is intended to be utilized with radio communication systems which comprise an electrically controlled antenna, for example in connection with a radar system or a mobile telephony system. The invention also relates to an arrangement for carrying out such a method.
In connection with radio communication systems, for example for radar applications, an antenna array is frequently utilized for transmitting and receiving radio signals. According to the prior art, such an antenna array can be constructed from a number of transceiver modules each of which comprises an antenna element, a controllable phase rotator and a controllable amplifier. The antenna elements can be made to cooperate as a unified antenna for transmission and, respectively, reception with sensitivity in the desired direction by arranging the antenna elements with a certain geometry and by suitable control of the said phase rotator and amplifier. Such an electrically controllable antenna, which does not comprise any moving parts, also provides the possibility of quickly redirecting the sensitivity of the antenna.
For a specific antenna, an antenna pattern with respect to, for example, transmission can be defined by distributing a common transmission signal to all transceiver modules of the antenna. The signals sent out, which are in phase with one another for a given direction, cooperate to produce a signal lobe whilst the signals for other directions are in opposite phase and thus cancel each other out. Between these two extreme cases, partial cancellation occurs to a varying degree. The resultant signal lobe as a function of directions can then be said to constitute the transmission pattern of the antenna. Both the direction and the shape of the transmission pattern can then be adapted to the current application of the antenna by suitably controlling the phase rotation and amplification of the respective transceiver module. The phase and amplitude values of this phase rotation and, respectively, amplification then constitute complex elements in the so-called control vector of the antenna pattern. This control vector is thus utilized for controlling the respective transceiver module, whereby a given antenna pattern is obtained.
In the case of reception with the antenna, the signals which are received at a respective module are, instead, summed to form a common input signal. In a corresponding manner as in the case of transmission with the antenna, a reception pattern is then defined by suitably controlling the phase rotation and amplification of the respective module.
An antenna pattern thus defines the gain of a given antenna as a function of the direction in space. In, for example, radar systems, an antenna pattern with a very high gain in a predetermined direction, the so-called main lobe, is normally aimed at. In the other antenna directions, the side lobes, as low a gain as possible is aimed at. In transmission, therefore, the signal sent out is to the highest possible degree concentrated in the main lobe and in reception, interfering signals in the side directions are avoided by minimizing the side lobe levels of the antenna.
In reception, an incoming signal is defined by summing the contributions from respective transceiver modules. Before the summing, the signals are normally weighted with a complex control vector which comprises parameters with respect to phase and amplification of a respective module. In so-called digital lobe shaping, which is a method which is known per se, this weighted summing is done digitally. More exactly, the analogue signals from a respective transceiver module are first analogue/digital converted, after which they are weighted with a vector and summed digitally. An advantage of digital lobe shaping is, for example, that the A/D-converted input signals can be stored in a memory for any subsequent signal processing. In this way, it is possible to study the received signals with different antenna patterns afterwards and by selecting different weighting functions. For example, the signal/noise ratio can be maximized in this way by looking for an optimum weighting function.
In an aeronautical radar system, for example, an active electrically controlled antenna array is normally used, which comprises a very large number of transceiver modules, of the order of 1000 or more. It would be desirable in itself to carry out digital lobe shaping of the signals from every one of these modules. However, such a method would require an A/D converter for every one of the transceiver modules. With today""s technology, such a system would be very cumbersome and costly, which is a disadvantage.
This problem can be partially solved by dividing the antenna into a number of smaller parts which in each case contain a certain number of transceiver modules. Such an arrangement, however, would entail certain problems, primarily in the form of so-called grating lobes. This means that the side lobe level of the antenna becomes drastically higher when the summing of the signal from the part-antennas is carried out with a weighting function, the phase gradient of which does not correspond to the phase gradients of the part antennas.
From patent document U.S. Pat. No. 5,764,187, a system for digital lobe shaping in transmission and reception by means of an antenna array is already known. In transmission, a signal in the respective transceiver module is modulated by means of phase rotators and amplifiers. In reception with the antenna, in contrast, time, phase and frequency information from the transmitter is utilized in a digital signal processing unit. The antenna can be controlled in such a manner that its aperture is divided up into different independent parts which then correspond to different lobes.
A problem which arises with this known system relates to the fact that the antenna comprises a number of transceiver modules, each one of which comprises an A/D converter. If the antenna is to comprise a very large number of transceiver modules, this would lead to disadvantages in the form of high cost and a high weight of the antenna according to what has been described above.
It is the aim of the present invention to obtain an improved method in radio communication, particularly in reception with an antenna array consisting of a large number of transceiver modules, whereby signals from different parts of the antenna or signals received from different directions can be separated and utilized for digital lobe shaping. This is achieved by means of a method, the characterizing features of which can be seen in Patent claim 1 following. The object is also achieved by means of an arrangement, the characterizing features of which can be seen in claim 8 following.
The invention consists of a method for radio communication with an electrically controlled antenna which comprises at least two transceiver modules which in each case comprise one antenna element, one controllable phase rotator and one controllable amplifier. The method according to the invention is utilized in reception with the antenna and comprises controlled phase rotation of a received signal in the respective transceiver module, controlled amplification of the received signal in the respective transceiver module, summing of the signals from the respective transceiver module, analogue/digital conversion of the summed signal, dividing up of the summed signal into at least two separable part-signals which correspond to different reception patterns of the antenna, and digital signal processing of the said part-signals. Furthermore, the invention comprises modulation of the said phase rotation and/or amplification with a predetermined code which corresponds to the respective part-signal and which is applied to the respective transceiver module before the said summing, and demodulation of the said analogue/digital-converted signal with a further code which is the inverse of the above-mentioned code. In this manner, the respective part-signals are separated.
By means of the invention, a number of advantages is achieved. Primarily, it may be noted that an antenna according to the invention can be constructed with a small number of A/D converters, which leads to cost and weight savings in comparison with the prior art. Moreover, the invention provides a possibility of instantaneously obtaining a number of antenna patterns with arbitrary directions in one and the same summation network with associated receivers. This is done by configuring the whole antenna in at least two different antenna patterns, whereby the said modulation is applied to the respective control vector for the differently configured antenna patterns, and by a corresponding demodulation with inverse codes which correspond to the different antenna patterns.
A particular advantage of the invention is that the said antenna can be reconfigured in a simple manner, that is to say the transceiver modules incorporated can be divided into different part-antennas with associated matching antenna patterns which can be selected, for example, in accordance with the operating condition of the radio communication system in question. This resetting is of particular interest in aeronautical radar systems since different antenna patterns can be utilized with different operating conditions of the aeroplane.
The term xe2x80x9ctransceiver modulexe2x80x9d means in this connection a transmitting and receiving unit which is included in an antenna and which comprises an antenna element, a controllable phase rotator and a controllable amplifier. The term xe2x80x9cchannelxe2x80x9d means in this connection a separately detectable signal path for received part-signals originating from different antenna patterns.